The present invention generally relates to manufacturing of electric and electronic apparatuses and more particularly to a solder alloy of various forms used for soldering electric and electronic components, as well as to a soldering process and further to a rig used for such a soldering process. In particular, the present invention relates to a lead-free solder alloy that contains no substantial amount of lead (Pb).
Solder alloys are characterized by low melting temperatures and provide excellent electric as well as mechanical properties. Thus, solder alloys of various forms, including solder powders and solder pastes, are used for mounting electronic components on a printed circuit board.
Meanwhile, conventional solder alloys contain Pb. As Pb is toxic against biological bodies, it has been necessary to take precautionary measure when conducting such a soldering process, while such a precautionary measure increases the cost of the products produced as a result of the soldering. Thus, there is a demand for a lead-free solder alloy that is suitable for use in various soldering processes including automated soldering process.
In the automated soldering process of electronic components, several types of solder alloys are used conventionally. A representative example is a solder alloy known as Sn63-Pb37, wherein the solder alloy contains 63 wt % of Sn and 37 wt % of Pb. This material causes an eutectic melting at a melting temperature of 183.degree. C. Another typical example is a solder alloy known as Sn62-Pb36-Ag2, wherein the solder alloy contains 62 wt % of Sn, 36 wt % of Pb and 2 wt % of Ag. The solder alloy forms an eutectic system characterized by a melting temperature of 179.degree. C. As these solder alloys have low melting temperatures and provide excellent mechanical properties in terms of tensile strength and elongation as well as excellent electrical properties such as low resistance, they are used extensively for various automated soldering processes.
Meanwhile, there is a tendency of increasing public regulations against the use of Pb in view of human health and in view of environmental protection. Under such circumstances, various efforts have been made for developing a substitute solder alloy that is free from Pb.
As the material for use in assembling electric and electronic apparatuses, such a substitute solder alloy is required to have a low melting temperature such that the soldered electric or electronic component experiences little degradation of performance caused by the heat at the time of soldering. Further, such a substitute solder alloy should have an excellent mechanical strength comparable to that of a conventional solder alloy that contains Pb.